Polyethylene-polybutadiene blends, process of curing, and products thereof



p 29, 1958 M. M. SAFFORD ET AL 2, POLYETHYLENE-POLYBUTADIENE BLENDSPROCESS OF CURING, AND PRODUCTS THEREOF Filed March. 27, 1956 E a w w wH w E U 0 w 0 n n r a 0 0 0 o 0 0 0 0 u. u u a D/CUMYL PE/POX/DEInventors-.-

Moyer M S'aff'ord,

Robert L. M

United States Patent C POLYETHYLENE-POLYBUTADIENE BLENDS, PROCESS OFCURIYG, AND PRODUCTS THEREOF Moyer M. Satford, Schenectady, and RobertL. Myers, Ballston Lake, N. Y., assignors to General Electric Company, acorporation of New York Application March 27, 1956, Serial No. 574,333

6 Claims. (Cl. 260-455) This invention relates to curable compositionscomprising blends of (1) polyethylene, (2) polymerized 1,3- butadiene(hereafter called polybutadiene), and (3) dia-cumyl peroxide, and thecured compositions thereof. More particularly, this invention relates toa method of curing blends of polyethylene and polybutadiene whichcomprises treating such blends with di-a-cumyl peroxide.

The features of this invention desired to be protected herein arepointed out with particularity in the appended claims. The inventionitself may be better understood by reference to the followingdescription taken in conjunction with the accompanying drawing.

In reference to the drawing, Figure 1 shown therein represents thetensile strengths at 30 C. and at 150 C. versus percent of di-a-cumylperoxide (also called di cumyl peroxide) of blends or polyethylene andalkali metal polybutadiene (hereafter defined) cured with dicnmylperoxide. Figure 2' represents the corresponding tensile strengthsobtained where emulsion polybutadiene (hereafter defined) is substitutedfor alkali metal polybutadiene in corresponding cured blends.

Among the polymeric materials which have evolved in recent years,polyethylene has proved to be one of the most popular. It has found wideusage as an insulating material, as a container material, as a conduitmaterial, etc. Fabrication, molding, extrusion and calendering ofpolyethylene are readily accomplished by standard methods, thusfacilitating its use for many purposes. Despite all this, however, theapplications of polyethylene are greatly limited by its lack of formstability; that is, the ability to retain a particular shape at elevatedtemperatures, and by its poor high temperature properties, such as poorhigh temperature tensile strength, tear strength, cut-through strength,etc.

One of the methods employed in improving the physical properties ofvarious polymers is the incorporation of fillers therein. Althoughmarked improvement in high temperature physical properties ofpolyethylene is noted when certain fillers are incorporated therein, thepresence fillers in polyethylene tends to diminish some of theelectrical properties of filled polyethylene as compared'to the unfilledpolymer. 1

We have now discovered that when polybutadiene is blended withpolyethylene and cured with di-u-cumyl peroxide, a product having hightemperature tensile strength and elongation and excellent electricalproperties is pro duced. This blend can be cured with di-ot-cumylperoxide within a short period of time, such as, for example, 15-30minutes to produce, by a short cure method anaemia"? to commercialproduction, a cured blend having excellent physical andelectrical'properties. predicted that the blend would cure within thisshort It could not have been period since as disclosed in the prior art,polybutadiene 1 could be cured by heat and peroxides only over extendedFurthermore, the uncured peroxide-- periods of time.

containing blend can be worked-at high temperatnres-,----

such as at C., at which temperature other peroxides "ice prematurelydecompose. In addition, because of this heat stability, the di-a-cumylperoxide-containing blends can be shipped in commerce withoutdeleterious efiects.

The blend of polyethylene and polybutadiene will hereafter be referredto as blends and the di-a-cumyl peroxide-cured blends as cumyl-curedblends.

In general, the invention can advantageously be carried out by millingpolybutadiene and polyethylene on differential rubber rolls (which canadvantageously be heated if desired) as dia-cumyl peroxide is added andintimately incorporated into the blend. Since it is more difiicult toobtain a homogeneous blend at lower temperatures, milling is generallycarried out at elevated temperatures, such as about IOU- C.

Thereupon, the blend can be fabricated, molded, extruded or calendered,etc., by suitable methods. The temperature at which the shapingoperation is effected can be varied widely depending on whether it isdesired that shaping and curing be accomplished in one operation. Ifdesired, the composition can be cured and shaped by a final heattreatment at about C. or higher but below the decomposition temperatureof the polymer. Curing ot the blend can be effected at ordinarypressures or at super-atmospheric pressure, such as from 10 to 1000pounds per square inch or more in the mold or press. If the surface curealone is desired without aifecting the interior, blends containing noperoxide may be extruded into a solution containing the peroxide, andthereupon heat-cured to produce a case hardened polymer. Thin films orfilaments extruded and heated in this manner will be sufficiently curedthroughout.

The polyethylene referred to herein is a solid poly? meric materialformed by either the high or low. pressure polymerization of ethylene."It is described in Patent 2,153,553-Fawcett et al., and in ModernPlastics Encyclopedia, New York, 1949, pp. 268-271. Specific examples ofcommercially available solid polyethylene are the polyethylene'sold byE. I. du Pont de Nemours & Co., Inc., Wilmington, Delaware, examples ofwhich are Alathons 1, 3, 10,12, 14, etc., those sold by the BakeliteCompany, such as DE-2400, DYNH, etc., and the low pressure PhillipsPetroleum Company polymers, such as Marlex 20, 50, etc. An excellentdiscussion of low pressuresolid polyethylene within the scope of thisinvention is found in Modern Plastics, vol. 33, #1 Sep tember 1955)commencing on page 85.

- 1,3-butadiene can enter into a polymer chain by either a 1,2 or1,4-mode of addition; the 1,2-mode of addition results in the followingdangling vinyl structure:

(hereafter called 1,2-polybutadiene), whereas the (hereafter "calledIA-polybutadiene). The types of catalysts are generally used topolymerize 1,3-butadiene,

"namely the free-radical and the alkali metal type catalyst. .6

When 1,3-butadieneispolymerized by free-radical type catalysts,such'a's' "peroxides, persulfates, etc. in an aqueous emulsion system, ahigher proportion of 1,4-poly- ,butadiene results as compared to thealkali metal type .catalyst wherein a higher proportion of1,2-polybutadiene is obtained. Using free-radical catalysts, one obtains-polybutadiene-having less than "25 %"l,'2=polyhutadiene.

Although blends of polyethylene and both alkali metal polymerizedbutadiene (also called alkali metal polybutadiene) and free-radicalpolymerized butadiene (also obtained by extrapolating the inherentviscosity v. concalled emulsion polybutadiene) can be cured withdi-ucumyl peroxide to products of improved properties, such centrationcurve to zero concentration.

The above described blends can be cured to products of this inventionwith di-u-cumyl peroxide,

as tensile strength, etc., blends of polyethylene and alkali 5 CH CHmetal polybutadiene can be cured with di-a-cumyl peroxide J: 3 (g 3 toproducts of more enhanced properties than the corre- Q- G spendingblends containing emulsion polybutadiene. This a ears to'be due to thefact that alkali metal olymerized biiiadiene, which containslargeramounts (ii dangling 1 .Whlch peroxide canfs Prepared m the.mam1er.descilbed vinyl groups (1,2-pdlybutadiene), is more reactive in the m92 et Journal of oligamc cliemlstry. presence of di-u-cumyl peroxidethan free-radical cured [SJ-1.62 (1950) i proportion peroxide tobuta'dien'e which has its residual double bonds buried in be viamdfiverdependmg the chain of the l4 polybutadiene' Thus in order to thecharacterlstlcs desired n the final product. Preferobtain the moreenhanced properties, such as high tensile l5 ably We employ the Peroxideamounis rangmg from strengths, it is necessary to employ polybumdiam com0.1 to 10 percentor higher based on weight of polymer. taminghigh-percentages of the 12 yp i. over 30% ()ptlmum properties and curmgtime are obtained with andprefembly 5O IOO% Lzwolybutadi-ene. about from1 to 7 percent of peroxide based on weight of Among the catalysts whichhave been usedare the alkali Polymer metals and compounds containingalkali metals. Thus, 0 In order that those skilled the art may undermetals, such as lithium, sodium, potassium, rubidium, stand the Presentmjvennon may pracnsed the cesium, sodium-potassium alloys, and compoundsof these following m glven by Way of luustfatwn and metals, such asphenyl isopropyl potassium, triphenyl not by Way of hmltanon' All Partsare y Welghtmethyl sodium, lithium butyl, arnyl sodium and the likeEXAMPLE compounds have been used to effect such polymerization.

Whereas free-radical catalysts tend to produce larger A rubbery polymerwas prepared from 1,3-butadiene amounts of 1,4-polybutadiene, catalystsof the alkalimetal and finely divided sodium using the techniquedescribed in type tend to increase the ratio of 1,2-polybutacliene.Marvel et al., J. Polymer Science I," p. 275 (1946). The However,temperature as well as catalysts affect the type following procedure wasemployed: Into clean dry bottles of polymer formed; for example,polybutadiene produced was placed 0.1 g. of finely divided sodiumdispersed in by polymerizing 1,3-butadiene with sodium at 110 C.toluene. Thereafter, 25 g. of 1,3-butadiene was charged contains about15% of the 1,2-polybutadiene, whereas as aliquid. A small amount of thebuta-diene was allowed 100% of 1,2-type polymer i produced when1,3-butadiene to evaporate to displace any air remaining in the bottle.is polymerized with sodium at 70 C. Although the The-bottles werecapped, and rotated at 30 C. for aperiod ratio of'the 1,2 to the1,4-polybutadiene can be determined of 48 hours. The residual catalystwas deactivated by by ozonization, probably the more accurate method ofdeadding 15 ml. of a 10% solution of absolute alcohol in termining thisratio is by the use of infra-red spectra. benzene. The rubber was recovy Precipitation from Infra-redcurves identifying the different types ofpolymers a benzene solution by addition of ethyl alcohol until the arefound in Dogadkin et al., Rubber Chemistry and polymer nolonger'precipitated. To this precipitated prod- Technology 24, pp.591-596 (1951), Hampton, Anal. 40 not was added 0.1% ofphenyl-p-naphthylamine as an Chem. 21, pp. 923-926 (1949), and Meyer,Ind. Eng. antioxidant. This unwashed polymer had an intrinsic vis-Chem.41,pp. 1570-1577 (1949). An excellent descripcosity of 6.0 whenmeasured in benzene solution. By tion of polybutadiene polymers is foundin Whitby, Syninfra-red analysis, this product contained at least 60% ofthetic Rubber," pp. 734-757, Wiley and Sons, N. Y. 1,2-polybutadiene.

(1954), wherein are described methods of preparing poly- EXAMPLE 2but'adiene falling within the scope of 'this-invention.

Since molecular weight is related to viscosity, viscosity Blends q 'p yhylen (Al'athon 10) and polybutadiene measurements are a convenientmethod of expressing (p p 1!! the manner of Example were P p y molecularweight l h polybutadiene gums 5f 3 milling together various ratios ofeach polymer on diller broad intrinsic viscosity range can be employed,we :ademi31mbb'eTTMb mated t0 0 Each p y y vantageously have employedpolybutadiene havingani'm polybutadiene blend was cured for 30 minutesat 170 C. trins'ic viscosity of I to 8 or higher. Optimum propertieswith y Peroxide based 011 total Weight of areobtai'ned usingp'olybutadiene having an intrinsic visboth polymers. Tensile strengthand percent elongation cosity of 3.0 to 6.0. r at both room temperature,'30 C. (Table I) and at 150 C.

Inherent viscosity is determined by a viscometer, such (Table *II) andpercent thermoplastic flow at 150 C. as an Ostwald viscometer on a 0.25percent solution of (Table III) were measured. Tensile strength inpounds polybutadiene in benzene. This value is calculated as the persquare inch (p. s. i.) and percent elongation were both naturallogarithm of the ratio of fiow time of the solumeasured according toASTM procedure, D-638-46T. tion to the flow time of the solvent dividedby the con- The results of these measurements are found in thefolcentration in grams/100 m1. Intrinsic viscosity [1 is lowin'gtables.

Table I TENSILE STRENGTH AND PERCENT ELONGATION AT ROOM TEMPERATUREPercent Dicumyl Peroxide Blend 95% Polrethvlenefitt -------'--iibilfi'ffii hi fi'flfii: b% l.".f: hi fi'ffiii ti Polyethylene, 20%Polybutadlene-..----- glliiiigl ibil 25%? S 60% Polyethylene,40%Polybutadlene Table II TENSILE STRENGTH AND PERCENT ELONGATION AT 150C.

Blend Percent Dioumyl Peroxide 95% Polyethylene, 5% Polybutadiene 300%80% Polyethylene, 20% Polybutadiene 60% Polyethylene, 40% Polybutadiene{550 p. s. i 100% 150 p. S. i 300 Table III THERMOPLASTIC PEBCEgl; OFLOWMEASUREMENT AT Percent Dicumyl Peroxide Blend 95% Polyethylene, 5%Polybutadiene Percent 3. 25

Percent Percent Percent Percent Polybutadiene 0. 5

Thermoplastic flow measurements were obtained in the following manner:

(1) A sample disk to be tested (approximately 0.225 inch thick) wasaccurately measured.

(2) Aluminum foil of .750 inch diameter was placed on each side of thesample disk.

(3) This was placed on a metal disk of the same size and heated in acirculating air oven in which the temperature could be accuratelycontrolled.

(4) The sample was preheated to the desired temperature for 5 minutes.

(5) A load of pounds per square inch was applied to the samples andreadings were taken on a micrometric gauge connected to the samplethrough the oven at 15, 30, 45, 60, 120, 180, 240, 300, and 360 seconds.

(6) The sample was removed after 6 minutes.

(7) The calculations were made as follows:

0. R.T. R.

O. T.original thickness (at room temperature) O. R.--thickness readingat 0 seconds after pressure applied (at tested temperature) T. R.--thickness reading after a specified time interval at tested temperature)X 100 thermoplastic flow From these tables it is noted that the hightemperature 'tensile strength and percent elongation of polyethylene aremarkedly improved by curing these blends with (11-0:- cumyl peroxide. Incontrast to polyethylene itself which is a liquid at 150 C., We havesucceeded in producing polyethylene possessing tensile strengths of over1000 .p. s. i. at a temperature (150 C.) at which polyethylene itselfnormally has no tensile strength. As demonstrated in Table III, thecured blends of this invention are not appreciably affected bythermoplastic deformation at high temperatures. As desired, theproperties of the ,cured blends can be varied over a wide range byvarying the ratio of each polymer and the amount of peroxide employed.Although we prefer to have at least 50% :polyethylene, lesser amounts ofpolyethylene; even as .low as "1% of polyethylene, can be used where amore rigid product is desired. Thus, the percent of polyethylene canrange from 195% based on total weight of polymer.

In order to compare electrical properties of the cured blend with fillercontaining polyethylene, the following compositions were prepared.

EXAMPLE 3 A composition comprising 87 parts of polyethylene (Alathon10), 10 parts of polybutadiene (Example 1), and 3 parts of di-a-cumylperoxide was prepared and cured by the method of Table I. The curedcomposition had a tensile strength C.) of 163 p. s. i., a percentelongation (135 C.) of 300%, and a percent thermoplastic fiow C.)of1.1%.

EXAMPLE 4 Another blend was prepared by a similar procedure of admixing77 parts of polyethylene (Alathon 10), 20 parts of polybutadiene(Example 1), and 3 parts of di-a-cumyl peroxide. The cured compositionhad a tensile strength (135 C.) of 400 p. s. i., a percent elongation(135 C.) of 200%, and a percent thermoplastic flow (150 C.) of 1.1%.

EXAMPLE 5 Polyethylene (Alathon 10, 76 parts), 20 parts of an aerosil(particle size 15-20 m and 4 parts of dicumyl I peroxide were blended ona rubber mill and cured in the manner of Examples 3 and 4. Theelectrical properties of the compositions of Ex- The tests used in TableIV were carried out according to the following ASTM measurements: powerfactor (F. F.) D-150-47T, dielectric constant (e') D-150-47T, lossfactor (e") D-150-47T, alternating current resistivity (AC D-257-46, anddirect current resistivity (DCp) D-257-46. I

From Table IV it is noted that the electrical properties of the cumylcured blends are superior to the electrical properties of thefiller-containing polyethylene. Al though the electrical properties ofthe cured blends are already superior to cured filled polyethylene,these properties can be further improved by washing polybutadiene priorto use in the blend. Where the sodium-type catalyst is deactivated withwater or alcohols and allowed to remain in polybutadiene, the product iscalled unwashed. Where the deactivated catalyst is removed by washingwith water, the product is called washed. As shown in application SerialNo. 574,332, assigned to the same assignee and filed of even date, theelectrical properties of washed polybutadiene are superior to unwashed.

An additional superiority of the cured blends to inorganicfiller-containing polyethylene is that the blends are less susceptibleto humidity from an electrical viewpoint.

EXAMPLE 6 Emulsion polybutadiene was prepared by adding 25 parts ofliquid 1,3-butadiene to a solution of 1.25 parts of soap flakes (IvoryFlakes), 0.3 part of potassium persulfate, and 0.5 part of dodecylmercaptan in 45 parts of water. The reaction vessel was rotatedcontinuously at 50 C. for 48 hours, then cooled to the temperature ofice-water, and the contents added with stirring to a concentratedaqueous solution (at C.) of sodium' chloride. Thereupon 200 cc. of a 2%H 50 solution was added to the slurry. After the pro-duct was freed ofacid and salts by water washings, water was removed by washing withalcohol and placing the resulting product in a desiccator for 48 hoursto remove the residual a1- cohol. An antioxidant,phenyl-fi-napthylamine, 0.1% based on polymer, was then milled into theproduct.

In addition to the method described in Example 6, emulsion polymerizedpolybutadiene can be prepared by other methods known to the art as, forexample, those methods disclosed in Whitby, Synthetic Rubber, John Wiley& Sons (1954), pp. 699-701.

EXAMPLE 7 Blends of polyethylene (Alathon l0) and emulsion polybutadiene(prepared in the manner of Example 6) were prepared by milling togethervarious ratios of each polymer on difierential rubber rolls heated to130 C. Each blend was cured for 30 minutes at 170 C. with 14 percentdi-a-cumyl peroxide based on total weight of both polymers. Tensilestrength and percent elongation at both room temperature of 30 C. (TableV) and at 150 C. (Table VI) were measured. Tensile strength inpounds'per square inch (p. s. i.) and percent elongation were measuredaccording to ASTM procedure, 13-638- 46T. These results are found in thefollowing tables (Tables V and VI).

Table V TENSILE STRENGTH AND PERCENT ELONGATION AT ROOM TEMPERATUREPercent Dicnmyl Peroxide Blend 957 Polyethylene 57 1,360 p. s. i 1.540p. s. i 1,700 p. s. i.

P olybutadiene. {15 a 200% 200%.

80% Polyethylene, {1,360 5 20% Polybutadiene.

By comparing Tables I and H (alkali metal polybutadiene) to Tables V andVI (emulsion polybutadiene), it is evident that blends of the former arecured to prod nets of higher tensile strengths than corresponding blendsof the latter.

The tensile strengths (30 C. and 150 C.) obtained by curing blends ofpolyethylene and alkali metal polybuta-diene with dicumyl peroxide werecompared with the tensile strengths of the corresponding blends of emulsion polybutadiene. These results are shown in the drawing. Figure 1represents the tensile strength (at 30 C. and 150 C.) of blends ofvarious proportions of polyethylene (Alathon 10) and alkali metalpolybutadiene (Example 1), cured by the method described in Example- 2with the percent of dicumyl peroxide designated on the graph. Curve Arepresents a blend of 95 parts of polyethylene and 5 parts ofpolybutadiene; curve B represents parts of polyethylene and 20 parts ofpolybutadiene; curve C represents 60 parts of polyethylene and 40 partsof polybutadiene.

Figure 2 represents the tensile strength (at 30 C. and 150 C.) of blendsof various proportions of polyethylene (Alathon l0) and emulsionpolybutadiene (Example 6) cured by the method described in Example 2with the percent dicumyl peroxide designated on the graph. Curve Drepresents a blend of parts of polyethylene and 5 parts of butadiene;curve E represents 80 parts of polyethylene and 20 parts ofpolybutadiene; curve F represents 60 parts of polyethylene and 40 partsof polybutadiene.

On comparing Fig. 1 with Fig. 2, it is evident that products of greatertensile strengths are produced when alkali metal polybutadiene is usedin the blend as compared to corresponding compositions containingemulsion polybutadiene.

Since the products of this invention have greater hot strength thanpolyethylene compositions previously described, they can be used inapplications where polyethylene itself has failed due to hightemperature form instability. Thus, these products can be used in hotstrength films or tapes for electrical insulations, for electricalparts, for example, spark plug caps, for insulating wire, for householdutensils which are used at elevated temperatures, for molded industrialparts which are subjected to high temperatures, for example, jet fuelcartridges, and the like, for industrial laminates, for conduits andcontains for hot liquids, etc. as well as for other uses which willappear to those skilled in the art.

Although the presence of fillers tends to diminish the electricalproperties, their presence is not precluded for certain applications.For example, conducting carbon blacks and metallic particles can beincorporated in these blends for strong but flexible heating pads andtapes. For other applications where electrical properties are ofsecondary importance, it may be desirable to add other fillers, such asfinely divided silica aerogels, xerogels, fumed silicas, such asaerosils, silicas rendered hydrophobic by surface treatment withalcohols in the manner of U. S. Patent 2,657,149-Iler, andtrialkylsilanes in the manner of Bueehe et al., Serial No. 531,829,filed August 31, 1955, and assigned to the same assignee as the presentapplication. Calcium silicates, aluminas, various kinds of carbon blackand other fillers can also be used. In addition, other modifying agents,such as dyes, pigments, stabilizers, plasticizers, antioxidants, etc.can also be added without departing from the scope of the invention. 7

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. A curable composition comprising blends of (1) solid polyethylene,(2) polymerized 1,3 butadiene containing at least 30% 1,2-polybutadiene,and (3) di'otcumyl peroxide.

2. The cured product of claim 1.

3. The composition of claim 1 in which the polymerized 1,3-butadienecomprises at least 50% 1,2-polybutadiene.

4. The cured product'of claim 3.

5. A process of curing blends of solid polyethylene and polybutadienecontaining at least 30% 1,2-polybutadiene which comprises heat curingsaid blends with di-ot-cumyl peroxide.

6. The process of claim 5 in which the polybutadiene comprises at least50% of 1,2-polybutadiene.

(References on following page) References Cited in the file of thispatent OTHER REFERENCES UNITED STATES PATENTS Karasch: Journal of Org.Chem. 15, pages 753-762,

2, 95 9 3 Macey May 20 1 2 Whltby: Synthenc Rubber, pages 734-757,copynght ..,61-, .80 May Sept. 30, 1952 5 7 1954 by John W11ey and Sons,New York, New York. 2,613,214 Plnkney et a1. Feb. 10, 1953 th Mar. 17,Braden et a Trans. Of the InStlt. Of e Rllbbfil Ind.,

31 (No. 6), pages 155165, December 1955. FOREIGN PATENTS 514,687 GreatBritain May 3, 1939

1. A CURABLE COMPOSITION COMPRISING BLENDS OF (1) SOLID POLYETHYLENE,(2) POLYMERIZED 1,3 BUTADIENE CONTAINING AT LEAST 30% 1,2-POLYBUTADIENE,AND (3) DI-ACUMYL PEROXIDE.